Optical combining device

ABSTRACT

An optical combining device for combining the paths of two light beams having different polarizations is provided. The device includes a scroll direction change prism and a polarized beam splitter. The scroll direction change prism is disposed in the path of a first light beam and changes a scroll direction of the first light beam to as to be the same as that of a second light beam. The polarized beam splitter is disposed in the path of both the first light beam, reflected from the scroll direction change prism, and the second light beam and combines the first and second beams by selectively transmitting or reflecting them according to the polarization direction thereof.

BACKGROUND OF THE INVENTION

This application claims the priority of Korean Patent Application No.2003-14003, filed on Mar. 6, 2003, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein in its entiretyby reference.

1. Field of the Invention

The present invention relates to an optical combining device which canimprove the optical efficiency of an optical system and be made compactby combining light beams proceeding along different paths.

2. Description of the Related Art

In general, a projection system provides an image by projecting an imagegenerated from a light valve, such as a liquid crystal display or adigital micromirror display, by using an additional light source onto ascreen.

A projection system is classified into a single panel type and a threepanel type according to the number of light valves. The single paneltype can make the structure of a projection system smaller than thethree panel type. However, since white light is separated into red,green, and blue (R, G, and B) colors in a sequential method, the opticalefficiency is lowered to ⅓ compared to the three panel type. Thus, thesingle panel type projection system requires improvement of the opticalefficiency.

In a typical single panel projection optical system, light radiated froma white light source is separated into three colors of R, G, and B byusing a color filter and the separated colors are sequentiallytransmitted to a light valve. The light valve is operated according tothe order of the colors to represent an image. Since the colors aresequentially processed in the single panel type optical system, theoptical efficiency is lowered to ⅓ compared to a three panel typeoptical system. To solve the above problem, a scrolling method has beensuggested. In a color scrolling method, white light is separated intothree colors of R, G, and B and simultaneously the separated colors aretransmitted to different positions of the light valve. Since an image isnot represented until all the R, G, and B colors arrive for each pixel,each of color bars is moved at a particular speed in a special method.

As shown in FIG. 1, in a conventional single panel type projectionsystem, white light which is not polarized is generated/radiated from alight source 11. The radiated white light passes through a fly eye lensarray 13 which mixes incident light to make a uniform light beam so thatthe white light becomes a uniform light beam and proceeds to apolarization changer 15. The polarization changer 15 changes thepolarization direction of the light beam so that the non-polarized whitelight radiated from the light source 11 becomes a white beam polarizedin one direction. The white beam passed through the polarization changer15 is split by first and second dichromatic mirrors 17 and 19 into red,blue, and green colors. That is, the first dichromatic mirror 17reflects light having a blue wavelength among the white beam incident onthe first dichromatic mirror 17 and transmits light having otherwavelengths. The light passed through the first dichromatic mirror 17 issplit by the second dichromatic mirror 19 into green and red lightbeams.

First through third scanning prisms 21, 23, and 25, for periodicallyscrolling an incident light beam, are arranged on an optical path ofeach split color. The first through third scanning prisms 21, 23, and 25each are prisms having a rectangular block shape and rotated by adriving source (not shown). As the angle made between the optical axisand the side surface of the prism changes on the optical path by therotation of each of the first through third scanning prisms 21, 23, and25, the proceeding path of the light beam passed through these prismsare changed periodically.

The initial angle of each prism is set such that, when the first throughthird scanning prisms 21, 23, and 25 are rotated on the optical path,the light beams passed through the respective first through thirdscanning prisms 21, 23, and 25 divide an effective image area of a lightvalve 33 into three sections. Accordingly, as shown in FIG. 2, accordingto the driving state of the first through third scanning prisms 21, 23,and 25, color bars are formed in the effective image area of the lightvalve 33 by repeating the order of (B, R, G)→(G, B, R)→(R, G, B).

The light beams passed through the first through third scanning prisms21, 23, and 25 are combined by third and fourth dichromatic mirrors 27and 29. Reflection mirrors 18 and 20 are arranged between the firstdichromatic mirror 17 and the third dichromatic mirror 27 and betweenthe second dichromatic mirror 19 and the fourth dichromatic mirror 29,respectively, so as to change the proceeding paths of the light beams.

The scrolled light beams passed through the fourth dichromatic mirror 29are incident on a polarized beam splitter 31 which transmits or reflectsthe incident light beam according to the polarization direction thereof.The light beam reflected by the polarized beam splitter 31 is incidenton the light valve 33 while the color bars are periodically scrolled asshown in FIG. 2. The light valve 33 generates an image from the incidentlight. The image is generated by making the polarization direction of anexit light beam different in units of pixels. This light beam having apolarization direction different from that of the incident light beam istransmitted through the polarized beam splitter 31 to proceed toward aprojection lens unit 35. The projection lens unit 35 magnifies the inputimage and projects the magnified image onto a screen 50.

The above-described projection device includes a plurality of relaylenses 41, 42, 43, 44, 45, 46, 47, 48, and 49 on the optical axis totransmit the light radiated from the light source 11 to the light valve33.

To represent a color image by using the scrolling method, the color barsneed to be moved at a constant speed as shown in FIG. 2. In theconventional structure, however, since the light valve and the threescanning prisms are synchronized for scrolling, the control ofsynchronization is difficult. In addition, since the scanning prisms 21,23, and 25 perform circular motions, the speed of the color scrolling isnot constant so that the quality of an image can be deteriorated.

SUMMARY OF THE INVENTION

To solve the above and other problems, the present invention provides anoptical combining device which combines light beams scrolled in twodifferent areas and proceeding on different optical paths to enhance theoptical efficiency.

According to an aspect of the present invention, an optical combiningdevice to make light beams having different polarization directions andproceeding along different paths proceed along the same path comprises ascroll direction change prism. The scroll direction change prism isarranged on a proceeding path of a first light beam of the light beamsproceeding along different paths and changes a scroll direction of thefirst light beam so as to be the same as that of a second light beamproceeding along a different path. The optical combining device alsocomprises a polarized beam splitter which is provided on a proceedingpath of the second light beam having a different polarization from thatof the first light beam and which makes the first and second light beamsproceed along the same path by selectively transmitting or reflecting anincident light beam according to the polarization direction thereof.

The scroll direction change prism comprises a first reflection surface,which receives and reflects the first light beam, and a secondreflection surface, which makes a right angle with the first reflectionsurface and which reflects an image of the first light beam reflected bythe first reflection surface reversely to proceed toward the polarizedbeam splitter.

According to another aspect of the present invention, an opticalcombining device comprises a scroll direction change prism, which isarranged on a proceeding path of a first light beam of light beamstransmitting different effective areas of a spiral lens disc and whichchanges a scroll direction of the first light beam so as to be the sameas that of a second light beam transmitting the other effective area.The optical combining device also comprises a beam shifter, which isarranged on a proceeding path of the second light beam and which shiftsthe second light beam so as to be combined with the first light beamexit from the scroll direction change prism.

The scroll direction change prism comprises a first reflection surface,which receives and reflects the first light beam, a second reflectionsurface which makes a right angel with the first reflection surface andwhich reflects an image of the light beam reflected by the firstreflection surface reversely, and a third reflection surface, whichreflects the light beam reflected by the second reflection surface in adirection parallel to the second light beam exit from the beam shifter.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a view illustrating the optical configuration of theconventional single panel type projection system;

FIG. 2 is a view illustrating the operation of the color scroll in theprojection system of FIG. 1;

FIG. 3 is a view illustrating the optical configuration of a projectionsystem adopting an optical combining device according to a firstexemplary embodiment of the present invention;

FIG. 4 is a perspective view illustrating the optical arrangement of thelight source and the color filter of FIG. 3;

FIG. 5 is a plan view illustrating the color filter of FIG. 4;

FIG. 6 is a front view illustrating the color filter of FIG. 4;

FIG. 7 is a view illustrating the optical operation of the beam splitterof FIG. 3;

FIG. 8 is a front view illustrating the spiral lens of FIG. 3;

FIG. 9 is a perspective view illustrating the spiral lens disc unit ofFIG. 3;

FIG. 10 is a perspective view illustrating an Amici prism used for theoptical combining device of FIG. 3;

FIG. 11 is a view illustrating a shifter used for the optical combiningdevice of FIG. 3;

FIG. 12 is a view illustrating a projection system adopting an opticalcombining device according to a second exemplary embodiment of thepresent invention; and

FIG. 13 is a view illustrating the optical combining device of FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 3, a projection system adopting an optical combiningdevice according to a first exemplary embodiment of the presentinvention includes a light source 60, a color filter 70 to separate alight beam radiated from the light source 60 according to apredetermined wavelength range, a spiral lens disc unit 100 toperiodically scroll a proceeding path of each of the light beamsseparated by the color filter 70, and a beam splitter 93 to magnify andsplit an incident light beam.

The light source 60 generates and radiates white light and includes alamp 61 to generate light and a reflection mirror 63 to reflect thelight radiated from the lamp 61 and guide the reflected light along aproceeding path thereof. The reflection mirror 63 may be an oval mirroror a parabolic mirror. The oval mirror has one focal point at theposition of the lamp 61 and the other focal point at a position wherelight is focused. The parabolic mirror makes the light radiated from thelamp 61 and reflected by the reflection mirror 63 a parallel beam. InFIG. 3, an oval mirror is employed as the reflection mirror 63.

The color filter 70 separates the incident light according to apredetermined wavelength range and makes the separated light beamsproceed at different angles. Thus, the color filter 70 prevents theincident light which is input at a predetermined angle from being outputin a direction other than a desired direction so that an efficiency inuse of light is improved. That is, an effect by a change in a value ofetendue which signifies a physical amount of optical conservation in anoptical system can be reduced.

To this end, the color filter 70, as shown in FIGS. 4 through 6,includes first, second, and third dichromatic prisms 79, 81, and 83 toseparate an incident light beam L into first, second, and third colorlight beams L1, L2, and L3 by reflecting light in a particularwavelength range and transmitting light in other wavelength range.

The first dichromatic prism 79 has a first mirror surface 80 arrangedinclined to an optical axis of the incident light beam L. The firstmirror surface 80 reflects the first color light beam L1 and transmitsthe second and third color light beams L2 and L3 of the incident lightbeam L. For example, the first mirror surface 80 reflects a light beamhaving a blue (B) wavelength and transmits light beams having differentwavelengths. The first dichromatic prism 79 has first reflectionsurfaces 79 a and 79 b (refer to FIG. 5) constituting an outer shapethereof and reflecting the incident light beam at a predetermined angle,inside the first dichromatic prism 79. In detail, the first reflectionsurfaces 79 a and 79 b totally reflect an incident light beam input atan angle greater than a predetermined angle, that is, a critical angle.Therefore, an efficiency in use of the incident light beam L can beimproved.

The second dichromatic prism 81 is arranged close to the firstdichromatic prism 79 and has a second mirror surface 82 arrangedinclined to the optical axis of the incident light beam L. The secondmirror surface 82 reflects the second color light beam L2, for example,a light beam having a red (R) wavelength, and transmits light beamshaving different wavelengths.

The third dichromatic prism 83 is arranged close to the seconddichromatic prism 81 and has a third mirror surface 84 arranged inclinedto the optical axis of the incident light beam L. The third mirrorsurface 84 reflects the third color light beam L3, for example, a lightbeam having a green (G) wavelength. The third mirror surface 83 can bereplaced with a total reflection mirror so as to reflect all theincident light beam.

The second and third dichromatic prisms 81 and 83 include the second andthird reflection surfaces 81 a and 81 b, and 83 a and 83 b,respectively. Since the second and third reflection surfaces 81 a and 81b, and 83 a and 83 b have the same functions as those of the firstreflection surfaces 79 a and 79 b, detailed descriptions thereof will beomitted herein.

The color filter 70 having the above structure is suitable for aprojection system using a micromirror device as a light valve to form animage regardless of the polarization property of the incident light.

The color filter 70 preferably, but not necessarily, further includes afirst collimating lens 71 to make the incident light a parallel beam ata position corresponding to a light incident surface of the firstdichromatic prism 79.

The color filter 70 preferably, but not necessarily, further includesfirst through third relay lenses 85, 86, and 87 arranged correspondingto the respective light exit surfaces of the first through thirddichromatic prisms 79, 81, and 83. The first through third relay senses85, 86, and 87 focus the first through third color light beams L1, L2,and L3 to have predetermined divergent angles.

The color filter 70 preferably, but not necessarily, further includesfirst and third polarized beam splitters 73 and 75 and a ½ wave plate 77disposed on an optical path between the first collimating lens 71 andthe first dichromatic prism 79.

The first polarized beam splitter 73 is provided at the light incidentsurface of the first dichromatic prism 79. The first polarized beamsplitter 73 transmits a first light beam having one polarization of theincident non-polarized white light to proceed toward the firstdichromatic prism 79 and reflects a second light beam having otherpolarization to proceed toward the second polarized beam splitter 75. Tothis end, the first polarized beam splitter 73 has a first polarizationsurface 74.

FIG. 6 shows that, when a white light beam in which a P polarization andan S polarization are mixed is radiated from the light source 60, thefirst polarization surface 74 transmits a light beam having the Ppolarization while reflecting a light beam having the S polarization.

The second polarized beam splitter 75 reflects a second light beamreflected by the first polarized beam splitter 73 to proceed toward thefirst dichromatic prism 79. Referring to FIG. 6, for example, the secondpolarized beam splitter 75 changes only a path of the S-polarized lightbeam without changing the polarization property thereof such that theS-polarized light beam can proceed parallel to the first light beamhaving been transmitted through the first polarized beam splitter 73. Tothis end, the second polarized beam splitter 75 has a secondpolarization surface 76 which reflects a light beam having a particularpolarization of the incident light, for example, the S-polarized lightbeam. The second polarized beam splitter 75 can be a total reflectionmirror which totally reflects the incident light.

The ½ wave plate 77 changes the phase of an incident light beam having apredetermined polarization by 180°. FIGS. 3 through 6 show an example inwhich the ½ wave plate 77 is arranged between the second polarized beamsplitter 75 and the first dichromatic prism 73 to change thepolarization direction of the second light beam to be the same as thatof the first light beam. That is, the S-polarized light beam reflectedby the second polarization surface 76 is changed to be the same as theP-polarized light beam which is the same as the polarization directionof the first light beam. Alternatively, the ½ wave plate 77 can bearranged between the first polarized beam splitter 73 and the firstdichromatic prism 79 to change the polarization direction of the firstlight beam to be the same as that of the second light beam.

Thus, the color filter 70 further including the first and secondpolarized beam splitters 73 and 75 can be used for a case in which anLCD is adopted as the light valve.

In the above color filter, the first through third dichromatic prisms79, 81, and 83 can be changed by those having a feature of transmittinga particular color light beam and reflecting other color light beams andthe optical arrangement thereof are changed suitable for the purpose.Since the manufacturing process of the first through third dichromaticprisms 79, 70, and 83 is widely known in the field of opticalapplication technology, a detailed description thereof will be omittedherein.

As shown in FIG. 3, a second collimating lens 91 to focus the firstthrough third color light beams L1, L2, and L3 which exit from the colorfilter 70 may be further provided on the optical path between the colorfilter 70 and the beam splitter 91.

The beam splitter 93 is arranged on the optical path between the secondcollimating lens 91 and the spiral lens disc unit 100 and split thelight beams, into at least two parts, which are separated into differentcolor light beams by the color filter 70 according to a predeterminedwavelength thereof and proceeding at different angles. That is, the beamsplitter 93 magnifies and separates the incident light beam to proceedtoward at least two effective areas of a spiral lens disc 101.

Referring to FIG. 7, the beam splitter 93 has an incident surface 93 aand an exit surface 93 b which have a “>” shaped section. The incidentsurface 93 a splits the incident light beam into at least two parts byrefracting each of the first through third color light beams L1, L2, andL3 in a direction far from the optical axis. The exit surface 93 brefracts the respective color light beams which are refracted at theincident surface 93 a in a direction of the optical axis so as to beparallel to the incident light beam. The beam split by refraction is dueto a difference in the refractive index between the beam splitter 93 andthe air and the geometrical arrangement.

Thus, by appropriately setting a refractive index n of the beam splitter93, an inclination angle θ of the incident surface 93 a and the exitsurface 93 b, and a thickness D between the incident surface 93 a andthe exit surface 93 b, all light beams can pass through first and thirdareas I and III corresponding to first and second effective areas A andB of FIG. 8 which are described later while a light beam is not incidenton a second area II corresponding to a driving source 105 of FIG. 9.Accordingly, by splitting the light beam using the beam splitter 91, theeffective light amount is increased and the first and second effectiveareas A and B of the spiral lens disc unit 100 can be utilized.

A plurality of cylindrical lenses 95 and 97 to shape the proceedinglight beams are arranged on the optical axes of the light beams splitinto two areas I and III by the beam splitter. Each of the cylindricallenses 95 and 97 correct the shape of the light beam by focusing theincident light beam in one direction and by linearly transmitting theincident light beam in the other direction, so as to shape the first andsecond effective areas A and B as indicated by a dotted line in FIG. 8.

Referring to FIGS. 8 and 9, the spiral lens disc unit 100 includes firstand second spiral lens discs 101 and 103 which are rotatable andsupported at a bracket 107, a glass rod 111 arranged on the optical pathbetween the first and second spiral lens discs 101 and 103, and adriving portion 105 which rotates the first and second spiral lens discs101 and 103.

At least one cylindrical lens cell 101 a and 103 a is spirally arrangedat least one surface of each of the first and second spiral lens discs101 and 103. The spiral lens discs 101 and 103, while rotating, changethe proceeding path of each of the light beams separated by the colorfilter 70 and periodically scroll the separated light beam. The scrolloperation of the spiral lens discs 101 and 103 are described in detailwith an exemplary case in which the first and second spiral lens discs101 and 103 rotate clockwise at a predetermined speed.

Each color light beam separated by the color filter 70 passes throughthe cylindrical lenses 95 and 97 to be shaped and passes through thefirst and second effective areas A and B. Each cylindrical lens cell 101a appears to be the same as a plurality of cylindrical lenses arrangedlinearly neighboring one another in view of the first effective area A.An effect that the cylindrical lenses are moved in a direction from theinner circumference to the outer circumference can be obtained. Thus,the color light beam incident on the first effective area A is scrolledfrom the inner circumference of the disc to the outer circumferencethereof. A color light beam incident on the second effective area B isscrolled by the same principle. However, the scroll directions of thelight beams in the first and second effective areas A and B are oppositeto each other.

The spiral lens disc unit 100 includes two discs: the first spiral lensdisc 101 scrolling an incident light beam and a second spiral lens disc103 arranged separated a predetermined distance from the first spirallens disc 101 and correcting a divergent angle of each of the lightbeams exit from the first spiral lens disc 101.

The glass rod 111 transfers the light beam exit from the first spirallens disc 101 to the second spiral lens disc 103 as it is. Also,considering the shape and the focal position of the color bar, a fly eyelens array 120, a cylindrical lens 131, and a fourth relay lens 161 arefurther provided.

The fly eye lens array 120 is arranged on an optical path of a lightbeam exit from the second spiral lens disc 103 and forms the color barby making the light beam passed through the spiral lens disc unit 100focused in different areas for each color. To this end, the fly eye lensarray 120 includes a first fly eye lens 121 having a plurality of convexportions formed in a two-dimensional array on an incident surface and/oran exit surface, and a second fly eye lens 123 arranged neighboring tothe first fly eye lens 121 and having a plurality of convex portionsformed in a two-dimensional array on an incident surface and/or an exitsurface. The first fly eye lens 25 is preferably, but not necessarilydisposed at a focal surface of the second spiral lens disc 103. Also,the convex portions of each of the first and second fly eye lenses 121and 123 are formed to match one-to-one with respect to the at least onecylindrical lens cell 101 a of the first and second spiral lens discs101 and 103 in the first and second effective areas A and B. Thus, eachof the color light beams scrolled by the spiral lens disc unit 100 aretransmitted by the first and second fly eye lens arrays 121 and 123 andare focused at different positions for each color so that the color barfor each color is formed.

The cylindrical lens 131 shapes the first through third color lightbeams separated for each color on the optical paths of the color lightbeams which have passed through the first and second effective areas Aand B and exit from the second fly eye lens 123.

An optical combining device 138 according to a first exemplaryembodiment of the present invention includes a scroll direction changeprism 140 to change the scroll direction so that the scroll directionsof the light beams passed through the first and second effective areas Aand B are the same, and a beam shifter 150 to combine the light beamssplit by the beam splitter 93 by shifting the same.

The scroll direction change prism 140 is arranged on the optical path ofthe light beams passed through one of the first and second effectiveareas A and B of the spiral lens disc unit 100 to change the scrolldirection. To this end, the scroll direction change prism 140 preferablyhas the shape of an Amici prism or penta prism.

Referring to FIG. 10, the scroll direction change prism 140 includes anincident surface 141 and an exit surface 147 through which the lightbeams passed through one of the first and second effective areas A andB, first and second reflection surfaces 143 a and 143 b arrangedperpendicularly to each other and inclined by an angle θ2 from theincident surface 141 toward the exit surface 147, and a third reflectionsurface 145 to reflect the light beam reflected by the first and secondreflection surfaces 143 a and 143 b to proceed toward the exit surface147. Thus, when a light beam having a scroll direction indicated by anarrow in FIG. 10 is incident on the incident surface 141, the verticaldirection of the incident light beam is not changed and the light beamproceeds toward the second reflection surface 143 b by being inclined bythe angle θ2. As a result, the scroll direction of the light beam ischanged to the opposite at the second reflection surface 143 b.Likewise, the light beam incident on the second reflection surface 143 bproceeds to the third reflection surface 145. When the light beam isreflected from the first reflection surface 143 a or the secondreflection surface 143 b and proceeds toward the third reflectionsurface 145, the scroll direction is reversed as indicated by the arrowsin the drawing.

Referring to FIG. 3, the beam shifter 150 may be a refractive opticalmember 151 having a rectangular shape arranged inclined on the opticalaxis. The refractive optical member 151 includes an incident surface 151a arranged inclined to an incident optical axis and an exit surface 151b arranged separated a predetermined distance from the incident surface151 a and parallel thereto. The refractive optical member 151 transmitsthe incident light beam refracted by a difference in the refractiveindex so as to shift the incident light beam toward the scroll directionchange prism 140.

Referring to FIG. 11, the beam shifter 150 may be a reflective opticalmember 153 which shifts an incident light beam by totally reflecting theincident light beam.

The reflective optical member 153 has an incident surface 153 a and anexit surface 153 b which make a right angle, and first and secondreflection surfaces 155 and 157 arranged inclined to the incidentoptical axis. The height Δd of the incident surface 153 a and of thefirst reflection surface 155 is sufficiently greater than the width ofthe incident light beam such that a light beam having a scroll directionindicated by a hollow arrow in the drawing can be shifted without achange in the scroll direction.

The fourth relay lens 161 is preferably arranged on the optical axisbetween the optical combining device 138 a and the light valve 165.

FIG. 12 shows a projection system adopting an optical combining deviceaccording to a second exemplary embodiment of the present invention. InFIG. 12, since the constituent elements having the same referencenumerals as those of the constituent elements shown in FIG. 3 have thesame structure and operation, detailed descriptions thereof are omittedherein.

The optical combining device 139 according to the second exemplaryembodiment of the present invention has a scroll direction change prism140 and a polarized beam splitter 146. The scroll direction change prism140, as shown in FIG. 13, includes an incident surface 141 and an exitsurface 147, which the first light beam I and the second light beam IIproceeding along different optical paths are incident on and exit from,and first and second reflection surfaces 143 a and 143 b arrangedinclined by an angle θ2 from the incident surface 141 toward the exitsurface 147. The polarized beam splitter 146 which reflects or transmitsthe incident light beam according to the polarization direction thereofis provided on the proceed paths of the first and second light beams Iand II.

By making the polarization directions of the first and second lightbeams I and II different, the first light beam I, which is reflected bythe first and second reflection surfaces 143 a and 143 b and hasreversed images, is reflected by the polarization beam splitter 146,while the second light beam is transmitted through the polarized beamsplitter 146. Thus, both the first and second light beams I and II endup on the same path. In order to make the polarization directions of thefirst and second light beams I and II different, as shown in FIG. 12, apolarization panel 94 is provided on an optical path of one of the firstand second light beams I and II between the beam splitter 93 and thecylindrical lens 95. The polarization panel 94 thus makes thepolarization directions of the first and second light beams I and IIdifferent from each other.

The first light beam I is reflected by the first and second reflectionsurfaces 143 a and 143 b and is incident on the polarized beam splitter146, with the direction of an image being reversed. The second lightbeam II is incident on the third polarized beam splitter 146 without achange in the direction of an image. For example, the first light beam Iis reflected by the third polarized beam splitter 146 while the secondlight beam II passes through the third polarized beam splitter 146, sothat the first and second light beams I and II proceed along the samepath. Thereby, the scroll directions of the first and second light beamsbecome the same.

Fourth relay lenses 261 and 263 are arranged on the proceeding paths ofthe first and second light beams I and II respectively passed throughthe first and second effective areas A and B. The fourth relay lenses261 and 263 are arranged at different positions to compensate for a pathdifference between the first and second light beams I and II.

As shown in FIGS. 3 and 12, in the projection system adopting theoptical combining device according to the present invention, the lightbeam scrolled by the rotation of the spiral lens disc unit 100 andcombined by a optical combining device 138 or 139 is processed by alight valve 165 or 270 according to an image signal to form an image.The light valve 165 may be a single unit of a reflective LCD device ashown in FIG. 3. When the light valve 165 is a reflective LCD device, abeam splitter 163 is provided in front of the light valve 165.Alternatively, as shown in FIG. 12, a micromirror device which generatesan image by modulating the scrolled light beam and reflects thegenerated image in a predetermined direction can be used as the lightvalve 270. The micromirror device 270 forms an image by varying areflection path of the incident light beam by driving a micromirror inunits of pixel. Since the structure of the micromirror device is wellknown, a detailed description thereof is omitted herein. The aboveexamples are merely examples of the light valves and two or more unitsof the reflective LCD devices can be provided.

The image formed by the light valves 165 and 270 is magnified andprojected by a projection lens unit 170 onto a screen 180.

As described above, in the optical combining device according to thepresent invention, by making the light beams proceeding along differentoptical paths proceed along one path, a system adopting the opticalcombining device can be made compact. For example, in a projectionsystem, when two areas of the spiral lens disc unit which scroll thecolor bar are used, the light beams passing through these two areasproceed on the same path and the scroll directions of one of the lightbeams is reversed, so that the directions which were opposite coincide.

Although the exemplary embodiments of the present invention have beendescribed, it will be understood by those skilled in the art that thepresent invention should not be limited to the described exemplaryembodiments, but that various changes and modifications can be madewithin the spirit and scope of the present invention. Accordingly, thescope of the present invention is not limited to the described range ofthe following claims.

1. An optical combining device to make light beams having differentpolarization directions and proceeding along different paths proceedalong the same path, the optical combining device comprising: a scrolldirection change prism which is arranged on a proceeding path of a firstlight beam of the light beams proceeding along different paths andchanges a scroll direction of the first light beam so as to be the sameas that of a second light beam proceeding along a different path; and apolarized beam splitter which is provided on a proceeding path of thesecond light beam having a different polarization from that of the firstlight beam and makes the first and second light beams proceed along thesame path by selectively transmitting or reflecting an incident lightbeam according to the polarization direction thereof.
 2. The opticalcombining device as claimed in claim 1, wherein the scroll directionchange prism comprises: a first reflection surface which receives andreflects the first light beam; and a second reflection surface whichmakes a right angle with the first reflection surface and reflects animage of the first light beam reflected by the first reflection surfacereversely to proceed toward the polarized beam splitter. 3-11.(canceled)